In a communication system, a receiver receives a radio-frequency (RF) signal from a transmitter, and down-converts the received signal from RF to base-band using one or more mixers. Each mixer mixes the received signal with a local oscillator (LO) signal. An LO buffer is typically provided to buffer the LO signal before the mixer.
There are several different circuit topologies for realizing a wireless device receiver. Some topologies involve a surface acoustic-wave (SAW) filter that is disposed in the incoming RF signal path between a low-noise amplifier (LNA) and a mixer. It is desirable to be able to realize a wireless device receiver of adequate performance without using the somewhat costly and large SAW device. In order to achieve good linearity in a SAW-less receiver, a purely passive down-converting mixer is sometimes used. The passive mixer does not have an active gm-cell, such as a gain stage before the mixer's switching core. It is, however, often difficult for this topology to meet demanding noise figure (NF) requirements while still achieving good linearity (e.g., triple beat) performance.
One current approach to achieve good NF performance is to use a 25-duty-cycle (25DC) LO in RF receivers for better gain. Another approach is the use of a higher duty-cycle LO, such as a 50DC LO, which reduces power consumption compared to a 25DC but comes at the cost of reduced gain.
Accordingly, there is a need in the art for reducing the power consumption in receivers of wireless devices while maintaining acceptable NF.